Fitting a "Marina" box to a 1098

[linearaudio]

Now I have the 940 head and free flowing exhaust fitted, my next quest is to fit a Marina derived overdrive box. The grand "Charliemorrisminor" has kindly supplied me with the info to sort the box out, and I have earmarked a Marina box/bellhousing, Triumph overdrive box and (hopefully!) Marina flywheel/ backplate. I am working on sourcing a clutch (any offers?) so will have the basic makings. Also about to get a shortened prop done, working on the length difference from backplate to output flange, as I want to be able to swap over with the least "downtime".

So... what pitfalls will I find regarding starter motor meshing, pilot bearing size, clutch operation (would like to maintain mechanical linkage of some kind ideally) and speedo drive ratio difference etc? I am fairly OK with the basic fitting as rear mounting/tunnel mods etc are in my information store.
Does anyone know the 1300 Marina tpm AND importantly the diff ratio, so I can work some figures out??

Oh, and there may be the puzzled ones who say "why not just fit a higher diff and forget the overdive?" I know that would make a lot of sense, but ultimately practical considerations aren't everything, or I would have put a 1275 lump in rather than modifying the head on the 1098!! I have a deep and meaningful relationship with "Molly" and want to do what she feels happy with (work that one out if you wear a white coat!)

[bmcecosse]

White coat will indeed be necessary i think. My 3.7 diff works beautifully with same spec engine as yours. It took not much more than an hour to fit............ remember that when you are struggling over several days (I suspect) to fit an o/d box!

[cormorant]

Hi BMC, you mean to say you run a 3.7 diff on a lightly modded 1098? I wouldn't have thought it would pull that up a long incline, for instance. I thought folks usually went for the 3.9. How much extra hp you getting out of your 1098 do you reckon?

[bmcecosse]

It pulls just fine - there will be times when I have to shift to third - so what - it's higher too! I doubt it has much more than maybe 55 or so ? 12G 940 head - slightly modified, single 38 HIF carb on alloy inlet - and now sporting 3 branch exhaust and big(ger) bore exhaust.
It's great - the 3.7 IS the one to go for - and there is a handy Mini speedo that slots straight in and keeps the speed and miles spot-on.

[cormorant]

Well that is a bit of a revelation because I have a 940 head, Marina manifold, 38hif on a manifold big bore exhaust all waiting to be fitted but I didn't think it would pull the 3.7. Was going to go for a 3.9 but now you have said that I will go for the 3.7 and not bother with my 5 speed /1275 plans. Thanks for that! Did you pocket the block or cut the seats deeper on the 940? And what is the tpm on the mini speedo please?

[bmcecosse]

The seats have been sunk 40 thou - BUT you may not need to do that (this head was originally on a Mini with higher lift cam) - so measure what you have - some heads don't need anything doing.
Mini speedo is 1248 tpm - works well. Mine was ~£5 including post on ebay!

[bmcecosse]

LA - don't rush into the prop shaft to quickly - you are likely to have to mount the engine slightly lower (shorten the towers) and maybe slightly forward to get the Marina box to clear the steering rack. So - don't make the prop shaft till you know the size for sure!

[cormorant]

Thanks for the info BM

[charlie_morris_minor]

I would feel uneasy about making your propshaft up now, they are not cheap, i would phone around and see how long it takes to get one knocked up after you place the order, it could be an expensive mistake..

[d_harris]

Incidentally, I have a 1248 tpm speedo going begging. Bit more than BMCs ebay bargain mind you...

[bmcecosse]

Ahh - but I'm just a pair auld retired scotsmun who has to eek out guid bargains for everything!